Merge branch 'master' into cq_create_api_changes

include/grpc++/impl/codegen/async_stream.h

@@ -101,6 +101,39 @@ class AsyncWriterInterface {
   /// \param[in] msg The message to be written.
   /// \param[in] tag The tag identifying the operation.
   virtual void Write(const W& msg, void* tag) = 0;
+
+  /// Request the writing of \a msg using WriteOptions \a options with
+  /// identifying tag \a tag.
+  ///
+  /// Only one write may be outstanding at any given time. This means that
+  /// after calling Write, one must wait to receive \a tag from the completion
+  /// queue BEFORE calling Write again.
+  /// WriteOptions \a options is used to set the write options of this message.
+  /// This is thread-safe with respect to \a Read
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] tag The tag identifying the operation.
+  virtual void Write(const W& msg, WriteOptions options, void* tag) = 0;
+
+  /// Request the writing of \a msg and coalesce it with the writing
+  /// of trailing metadata, using WriteOptions \a options with identifying tag
+  /// \a tag.
+  ///
+  /// For client, WriteLast is equivalent of performing Write and WritesDone in
+  /// a single step.
+  /// For server, WriteLast buffers the \a msg. The writing of \a msg is held
+  /// until Finish is called, where \a msg and trailing metadata are coalesced
+  /// and write is initiated. Note that WriteLast can only buffer \a msg up to
+  /// the flow control window size. If \a msg size is larger than the window
+  /// size, it will be sent on wire without buffering.
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] tag The tag identifying the operation.
+  void WriteLast(const W& msg, WriteOptions options, void* tag) {
+    Write(msg, options.set_last_message(), tag);
+  }
 };
 
 template <class R>
@@ -183,11 +216,17 @@ class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
       : context_(context), call_(channel->CreateCall(method, context, cq)) {
     finish_ops_.RecvMessage(response);
     finish_ops_.AllowNoMessage();
-
-    init_ops_.set_output_tag(tag);
-    init_ops_.SendInitialMetadata(context->send_initial_metadata_,
-                                  context->initial_metadata_flags());
-    call_.PerformOps(&init_ops_);
+    // if corked bit is set in context, we buffer up the initial metadata to
+    // coalesce with later message to be sent. No op is performed.
+    if (context_->initial_metadata_corked_) {
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+    } else {
+      write_ops_.set_output_tag(tag);
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+      call_.PerformOps(&write_ops_);
+    }
   }
 
   void ReadInitialMetadata(void* tag) override {
@@ -205,10 +244,21 @@ class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      write_ops_.ClientSendClose();
+    }
+    // TODO(ctiller): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
   void WritesDone(void* tag) override {
-    writes_done_ops_.set_output_tag(tag);
-    writes_done_ops_.ClientSendClose();
-    call_.PerformOps(&writes_done_ops_);
+    write_ops_.set_output_tag(tag);
+    write_ops_.ClientSendClose();
+    call_.PerformOps(&write_ops_);
   }
 
   void Finish(Status* status, void* tag) override {
@@ -223,10 +273,9 @@ class ClientAsyncWriter final : public ClientAsyncWriterInterface<W> {
  private:
   ClientContext* context_;
   Call call_;
-  CallOpSet<CallOpSendInitialMetadata> init_ops_;
   CallOpSet<CallOpRecvInitialMetadata> meta_ops_;
-  CallOpSet<CallOpSendMessage> write_ops_;
-  CallOpSet<CallOpClientSendClose> writes_done_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose>
+      write_ops_;
   CallOpSet<CallOpRecvInitialMetadata, CallOpGenericRecvMessage,
             CallOpClientRecvStatus>
       finish_ops_;
@@ -253,10 +302,17 @@ class ClientAsyncReaderWriter final
                           const RpcMethod& method, ClientContext* context,
                           void* tag)
       : context_(context), call_(channel->CreateCall(method, context, cq)) {
-    init_ops_.set_output_tag(tag);
-    init_ops_.SendInitialMetadata(context->send_initial_metadata_,
-                                  context->initial_metadata_flags());
-    call_.PerformOps(&init_ops_);
+    if (context_->initial_metadata_corked_) {
+      // if corked bit is set in context, we buffer up the initial metadata to
+      // coalesce with later message to be sent. No op is performed.
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+    } else {
+      write_ops_.set_output_tag(tag);
+      write_ops_.SendInitialMetadata(context->send_initial_metadata_,
+                                     context->initial_metadata_flags());
+      call_.PerformOps(&write_ops_);
+    }
   }
 
   void ReadInitialMetadata(void* tag) override {
@@ -283,10 +339,21 @@ class ClientAsyncReaderWriter final
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      write_ops_.ClientSendClose();
+    }
+    // TODO(ctiller): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
   void WritesDone(void* tag) override {
-    writes_done_ops_.set_output_tag(tag);
-    writes_done_ops_.ClientSendClose();
-    call_.PerformOps(&writes_done_ops_);
+    write_ops_.set_output_tag(tag);
+    write_ops_.ClientSendClose();
+    call_.PerformOps(&write_ops_);
   }
 
   void Finish(Status* status, void* tag) override {
@@ -301,11 +368,10 @@ class ClientAsyncReaderWriter final
  private:
   ClientContext* context_;
   Call call_;
-  CallOpSet<CallOpSendInitialMetadata> init_ops_;
   CallOpSet<CallOpRecvInitialMetadata> meta_ops_;
   CallOpSet<CallOpRecvInitialMetadata, CallOpRecvMessage<R>> read_ops_;
-  CallOpSet<CallOpSendMessage> write_ops_;
-  CallOpSet<CallOpClientSendClose> writes_done_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage, CallOpClientSendClose>
+      write_ops_;
   CallOpSet<CallOpRecvInitialMetadata, CallOpClientRecvStatus> finish_ops_;
 };
 
@@ -395,6 +461,20 @@ class ServerAsyncWriterInterface : public ServerAsyncStreamingInterface,
                                    public AsyncWriterInterface<W> {
  public:
   virtual void Finish(const Status& status, void* tag) = 0;
+
+  /// Request the writing of \a msg and coalesce it with trailing metadata which
+  /// contains \a status, using WriteOptions options with identifying tag \a
+  /// tag.
+  ///
+  /// WriteAndFinish is equivalent of performing WriteLast and Finish in a
+  /// single step.
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] status The Status that server returns to client.
+  /// \param[in] tag The tag identifying the operation.
+  virtual void WriteAndFinish(const W& msg, WriteOptions options,
+                              const Status& status, void* tag) = 0;
 };
 
 template <class W>
@@ -418,29 +498,37 @@ class ServerAsyncWriter final : public ServerAsyncWriterInterface<W> {
 
   void Write(const W& msg, void* tag) override {
     write_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      write_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                     ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        write_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&write_ops_);
     // TODO(ctiller): don't assert
     GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg).ok());
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
+
+    EnsureInitialMetadataSent(&write_ops_);
+    // TODO(ctiller): don't assert
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
+  void WriteAndFinish(const W& msg, WriteOptions options, const Status& status,
+                      void* tag) override {
+    write_ops_.set_output_tag(tag);
+    EnsureInitialMetadataSent(&write_ops_);
+    options.set_buffer_hint();
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    write_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
+    call_.PerformOps(&write_ops_);
+  }
+
   void Finish(const Status& status, void* tag) override {
     finish_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      finish_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                      ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        finish_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&finish_ops_);
     finish_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
     call_.PerformOps(&finish_ops_);
   }
@@ -448,10 +536,24 @@ class ServerAsyncWriter final : public ServerAsyncWriterInterface<W> {
  private:
   void BindCall(Call* call) override { call_ = *call; }
 
+  template <class T>
+  void EnsureInitialMetadataSent(T* ops) {
+    if (!ctx_->sent_initial_metadata_) {
+      ops->SendInitialMetadata(ctx_->initial_metadata_,
+                               ctx_->initial_metadata_flags());
+      if (ctx_->compression_level_set()) {
+        ops->set_compression_level(ctx_->compression_level());
+      }
+      ctx_->sent_initial_metadata_ = true;
+    }
+  }
+
   Call call_;
   ServerContext* ctx_;
   CallOpSet<CallOpSendInitialMetadata> meta_ops_;
-  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> write_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+            CallOpServerSendStatus>
+      write_ops_;
   CallOpSet<CallOpSendInitialMetadata, CallOpServerSendStatus> finish_ops_;
 };
 
@@ -462,6 +564,20 @@ class ServerAsyncReaderWriterInterface : public ServerAsyncStreamingInterface,
                                          public AsyncReaderInterface<R> {
  public:
   virtual void Finish(const Status& status, void* tag) = 0;
+
+  /// Request the writing of \a msg and coalesce it with trailing metadata which
+  /// contains \a status, using WriteOptions options with identifying tag \a
+  /// tag.
+  ///
+  /// WriteAndFinish is equivalent of performing WriteLast and Finish in a
+  /// single step.
+  ///
+  /// \param[in] msg The message to be written.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  /// \param[in] status The Status that server returns to client.
+  /// \param[in] tag The tag identifying the operation.
+  virtual void WriteAndFinish(const W& msg, WriteOptions options,
+                              const Status& status, void* tag) = 0;
 };
 
 template <class W, class R>
@@ -492,29 +608,36 @@ class ServerAsyncReaderWriter final
 
   void Write(const W& msg, void* tag) override {
     write_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      write_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                     ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        write_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&write_ops_);
     // TODO(ctiller): don't assert
     GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg).ok());
     call_.PerformOps(&write_ops_);
   }
 
+  void Write(const W& msg, WriteOptions options, void* tag) override {
+    write_ops_.set_output_tag(tag);
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
+    EnsureInitialMetadataSent(&write_ops_);
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    call_.PerformOps(&write_ops_);
+  }
+
+  void WriteAndFinish(const W& msg, WriteOptions options, const Status& status,
+                      void* tag) override {
+    write_ops_.set_output_tag(tag);
+    EnsureInitialMetadataSent(&write_ops_);
+    options.set_buffer_hint();
+    GPR_CODEGEN_ASSERT(write_ops_.SendMessage(msg, options).ok());
+    write_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
+    call_.PerformOps(&write_ops_);
+  }
+
   void Finish(const Status& status, void* tag) override {
     finish_ops_.set_output_tag(tag);
-    if (!ctx_->sent_initial_metadata_) {
-      finish_ops_.SendInitialMetadata(ctx_->initial_metadata_,
-                                      ctx_->initial_metadata_flags());
-      if (ctx_->compression_level_set()) {
-        finish_ops_.set_compression_level(ctx_->compression_level());
-      }
-      ctx_->sent_initial_metadata_ = true;
-    }
+    EnsureInitialMetadataSent(&finish_ops_);
+
     finish_ops_.ServerSendStatus(ctx_->trailing_metadata_, status);
     call_.PerformOps(&finish_ops_);
   }
@@ -524,11 +647,25 @@ class ServerAsyncReaderWriter final
 
   void BindCall(Call* call) override { call_ = *call; }
 
+  template <class T>
+  void EnsureInitialMetadataSent(T* ops) {
+    if (!ctx_->sent_initial_metadata_) {
+      ops->SendInitialMetadata(ctx_->initial_metadata_,
+                               ctx_->initial_metadata_flags());
+      if (ctx_->compression_level_set()) {
+        ops->set_compression_level(ctx_->compression_level());
+      }
+      ctx_->sent_initial_metadata_ = true;
+    }
+  }
+
   Call call_;
   ServerContext* ctx_;
   CallOpSet<CallOpSendInitialMetadata> meta_ops_;
   CallOpSet<CallOpRecvMessage<R>> read_ops_;
-  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> write_ops_;
+  CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+            CallOpServerSendStatus>
+      write_ops_;
   CallOpSet<CallOpSendInitialMetadata, CallOpServerSendStatus> finish_ops_;
 };
 

include/grpc++/impl/codegen/call.h

@@ -84,8 +84,9 @@ inline grpc_metadata* FillMetadataArray(
 /// Per-message write options.
 class WriteOptions {
  public:
-  WriteOptions() : flags_(0) {}
-  WriteOptions(const WriteOptions& other) : flags_(other.flags_) {}
+  WriteOptions() : flags_(0), last_message_(false) {}
+  WriteOptions(const WriteOptions& other)
+      : flags_(other.flags_), last_message_(other.last_message_) {}
 
   /// Clear all flags.
   inline void Clear() { flags_ = 0; }
@@ -141,6 +142,43 @@ class WriteOptions {
   /// \sa GRPC_WRITE_BUFFER_HINT
   inline bool get_buffer_hint() const { return GetBit(GRPC_WRITE_BUFFER_HINT); }
 
+  /// corked bit: aliases set_buffer_hint currently, with the intent that
+  /// set_buffer_hint will be removed in the future
+  inline WriteOptions& set_corked() {
+    SetBit(GRPC_WRITE_BUFFER_HINT);
+    return *this;
+  }
+
+  inline WriteOptions& clear_corked() {
+    ClearBit(GRPC_WRITE_BUFFER_HINT);
+    return *this;
+  }
+
+  inline bool is_corked() const { return GetBit(GRPC_WRITE_BUFFER_HINT); }
+
+  /// last-message bit: indicates this is the last message in a stream
+  /// client-side:  makes Write the equivalent of performing Write, WritesDone
+  /// in a single step
+  /// server-side:  hold the Write until the service handler returns (sync api)
+  /// or until Finish is called (async api)
+  inline WriteOptions& set_last_message() {
+    last_message_ = true;
+    return *this;
+  }
+
+  /// Clears flag indicating that this is the last message in a stream,
+  /// disabling coalescing.
+  inline WriteOptions& clear_last_messsage() {
+    last_message_ = false;
+    return *this;
+  }
+
+  /// Get value for the flag indicating that this is the last message, and
+  /// should be coalesced with trailing metadata.
+  ///
+  /// \sa GRPC_WRITE_LAST_MESSAGE
+  bool is_last_message() const { return last_message_; }
+
   WriteOptions& operator=(const WriteOptions& rhs) {
     flags_ = rhs.flags_;
     return *this;
@@ -154,6 +192,7 @@ class WriteOptions {
   bool GetBit(const uint32_t mask) const { return (flags_ & mask) != 0; }
 
   uint32_t flags_;
+  bool last_message_;
 };
 
 /// Default argument for CallOpSet. I is unused by the class, but can be
@@ -224,7 +263,7 @@ class CallOpSendMessage {
   /// after use.
   template <class M>
   Status SendMessage(const M& message,
-                     const WriteOptions& options) GRPC_MUST_USE_RESULT;
+                     WriteOptions options) GRPC_MUST_USE_RESULT;
 
   template <class M>
   Status SendMessage(const M& message) GRPC_MUST_USE_RESULT;
@@ -252,8 +291,7 @@ class CallOpSendMessage {
 };
 
 template <class M>
-Status CallOpSendMessage::SendMessage(const M& message,
-                                      const WriteOptions& options) {
+Status CallOpSendMessage::SendMessage(const M& message, WriteOptions options) {
   write_options_ = options;
   return SerializationTraits<M>::Serialize(message, &send_buf_, &own_buf_);
 }

include/grpc++/impl/codegen/client_context.h

@@ -281,6 +281,17 @@ class ClientContext {
   /// \param algorithm The compression algorithm used for the client call.
   void set_compression_algorithm(grpc_compression_algorithm algorithm);
 
+  /// Flag whether the initial metadata should be \a corked
+  ///
+  /// If \a corked is true, then the initial metadata will be colasced with the
+  /// write of first message in the stream.
+  ///
+  /// \param corked The flag indicating whether the initial metadata is to be
+  /// corked or not.
+  void set_initial_metadata_corked(bool corked) {
+    initial_metadata_corked_ = corked;
+  }
+
   /// Return the peer uri in a string.
   ///
   /// \warning This value is never authenticated or subject to any security
@@ -357,7 +368,8 @@ class ClientContext {
            (cacheable_ ? GRPC_INITIAL_METADATA_CACHEABLE_REQUEST : 0) |
            (wait_for_ready_explicitly_set_
                 ? GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET
-                : 0);
+                : 0) |
+           (initial_metadata_corked_ ? GRPC_INITIAL_METADATA_CORKED : 0);
   }
 
   grpc::string authority() { return authority_; }
@@ -384,6 +396,7 @@ class ClientContext {
   PropagationOptions propagation_options_;
 
   grpc_compression_algorithm compression_algorithm_;
+  bool initial_metadata_corked_;
 };
 
 }  // namespace grpc

include/grpc++/impl/codegen/sync_stream.h

@@ -100,22 +100,40 @@ class WriterInterface {
  public:
   virtual ~WriterInterface() {}
 
-  /// Blocking write \a msg to the stream with options.
+  /// Blocking write \a msg to the stream with WriteOptions \a options.
   /// This is thread-safe with respect to \a Read
   ///
   /// \param msg The message to be written to the stream.
-  /// \param options Options affecting the write operation.
+  /// \param options The WriteOptions affecting the write operation.
   ///
   /// \return \a true on success, \a false when the stream has been closed.
-  virtual bool Write(const W& msg, const WriteOptions& options) = 0;
+  virtual bool Write(const W& msg, WriteOptions options) = 0;
 
-  /// Blocking write \a msg to the stream with default options.
+  /// Blocking write \a msg to the stream with default write options.
   /// This is thread-safe with respect to \a Read
   ///
   /// \param msg The message to be written to the stream.
   ///
   /// \return \a true on success, \a false when the stream has been closed.
   inline bool Write(const W& msg) { return Write(msg, WriteOptions()); }
+
+  /// Write \a msg and coalesce it with the writing of trailing metadata, using
+  /// WriteOptions \a options.
+  ///
+  /// For client, WriteLast is equivalent of performing Write and WritesDone in
+  /// a single step. \a msg and trailing metadata are coalesced and sent on wire
+  /// by calling this function.
+  /// For server, WriteLast buffers the \a msg. The writing of \a msg is held
+  /// until the service handler returns, where \a msg and trailing metadata are
+  /// coalesced and sent on wire. Note that WriteLast can only buffer \a msg up
+  /// to the flow control window size. If \a msg size is larger than the window
+  /// size, it will be sent on wire without buffering.
+  ///
+  /// \param[in] msg The message to be written to the stream.
+  /// \param[in] options The WriteOptions to be used to write this message.
+  void WriteLast(const W& msg, WriteOptions options) {
+    Write(msg, options.set_last_message());
+  }
 };
 
 /// Client-side interface for streaming reads of message of type \a R.
@@ -217,11 +235,13 @@ class ClientWriter : public ClientWriterInterface<W> {
     finish_ops_.RecvMessage(response);
     finish_ops_.AllowNoMessage();
 
-    CallOpSet<CallOpSendInitialMetadata> ops;
-    ops.SendInitialMetadata(context->send_initial_metadata_,
-                            context->initial_metadata_flags());
-    call_.PerformOps(&ops);
-    cq_.Pluck(&ops);
+    if (!context_->initial_metadata_corked_) {
+      CallOpSet<CallOpSendInitialMetadata> ops;
+      ops.SendInitialMetadata(context->send_initial_metadata_,
+                              context->initial_metadata_flags());
+      call_.PerformOps(&ops);
+      cq_.Pluck(&ops);
+    }
   }
 
   void WaitForInitialMetadata() {
@@ -234,11 +254,24 @@ class ClientWriter : public ClientWriterInterface<W> {
   }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
-    CallOpSet<CallOpSendMessage> ops;
+  bool Write(const W& msg, WriteOptions options) override {
+    CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+              CallOpClientSendClose>
+        ops;
+
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      ops.ClientSendClose();
+    }
+    if (context_->initial_metadata_corked_) {
+      ops.SendInitialMetadata(context_->send_initial_metadata_,
+                              context_->initial_metadata_flags());
+      context_->set_initial_metadata_corked(false);
+    }
     if (!ops.SendMessage(msg, options).ok()) {
       return false;
     }
+
     call_.PerformOps(&ops);
     return cq_.Pluck(&ops);
   }
@@ -297,13 +330,15 @@ class ClientReaderWriter final : public ClientReaderWriterInterface<W, R> {
   ClientReaderWriter(ChannelInterface* channel, const RpcMethod& method,
                      ClientContext* context)
       : context_(context),
-        cq_(true),  // Pluckable cq
+        cq_(true), // Pluckable cq
         call_(channel->CreateCall(method, context, &cq_)) {
-    CallOpSet<CallOpSendInitialMetadata> ops;
-    ops.SendInitialMetadata(context->send_initial_metadata_,
-                            context->initial_metadata_flags());
-    call_.PerformOps(&ops);
-    cq_.Pluck(&ops);
+    if (!context_->initial_metadata_corked_) {
+      CallOpSet<CallOpSendInitialMetadata> ops;
+      ops.SendInitialMetadata(context->send_initial_metadata_,
+                              context->initial_metadata_flags());
+      call_.PerformOps(&ops);
+      cq_.Pluck(&ops);
+    }
   }
 
   void WaitForInitialMetadata() override {
@@ -331,9 +366,24 @@ class ClientReaderWriter final : public ClientReaderWriterInterface<W, R> {
   }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
-    CallOpSet<CallOpSendMessage> ops;
-    if (!ops.SendMessage(msg, options).ok()) return false;
+  bool Write(const W& msg, WriteOptions options) override {
+    CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage,
+              CallOpClientSendClose>
+        ops;
+
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+      ops.ClientSendClose();
+    }
+    if (context_->initial_metadata_corked_) {
+      ops.SendInitialMetadata(context_->send_initial_metadata_,
+                              context_->initial_metadata_flags());
+      context_->set_initial_metadata_corked(false);
+    }
+    if (!ops.SendMessage(msg, options).ok()) {
+      return false;
+    }
+
     call_.PerformOps(&ops);
     return cq_.Pluck(&ops);
   }
@@ -429,7 +479,10 @@ class ServerWriter final : public ServerWriterInterface<W> {
   }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
+  bool Write(const W& msg, WriteOptions options) override {
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
     CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> ops;
     if (!ops.SendMessage(msg, options).ok()) {
       return false;
@@ -491,7 +544,10 @@ class ServerReaderWriterBody final {
     return call_->cq()->Pluck(&ops) && ops.got_message;
   }
 
-  bool Write(const W& msg, const WriteOptions& options) {
+  bool Write(const W& msg, WriteOptions options) {
+    if (options.is_last_message()) {
+      options.set_buffer_hint();
+    }
     CallOpSet<CallOpSendInitialMetadata, CallOpSendMessage> ops;
     if (!ops.SendMessage(msg, options).ok()) {
       return false;
@@ -529,7 +585,7 @@ class ServerReaderWriter final : public ServerReaderWriterInterface<W, R> {
   bool Read(R* msg) override { return body_.Read(msg); }
 
   using WriterInterface<W>::Write;
-  bool Write(const W& msg, const WriteOptions& options) override {
+  bool Write(const W& msg, WriteOptions options) override {
     return body_.Write(msg, options);
   }
 
@@ -568,8 +624,7 @@ class ServerUnaryStreamer final
   }
 
   using WriterInterface<ResponseType>::Write;
-  bool Write(const ResponseType& response,
-             const WriteOptions& options) override {
+  bool Write(const ResponseType& response, WriteOptions options) override {
     if (write_done_ || !read_done_) {
       return false;
     }
@@ -610,8 +665,7 @@ class ServerSplitStreamer final
   }
 
   using WriterInterface<ResponseType>::Write;
-  bool Write(const ResponseType& response,
-             const WriteOptions& options) override {
+  bool Write(const ResponseType& response, WriteOptions options) override {
     return read_done_ && body_.Write(response, options);
   }
 

include/grpc/impl/codegen/grpc_types.h

@@ -316,13 +316,16 @@ typedef enum grpc_call_error {
 /** Signal that GRPC_INITIAL_METADATA_WAIT_FOR_READY was explicitly set
     by the calling application. */
 #define GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET (0x00000080u)
+/** Signal that the initial metadata should be corked */
+#define GRPC_INITIAL_METADATA_CORKED (0x00000100u)
 
 /** Mask of all valid flags */
-#define GRPC_INITIAL_METADATA_USED_MASK       \
-  (GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST | \
-   GRPC_INITIAL_METADATA_WAIT_FOR_READY |     \
-   GRPC_INITIAL_METADATA_CACHEABLE_REQUEST |  \
-   GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET)
+#define GRPC_INITIAL_METADATA_USED_MASK                  \
+  (GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST |            \
+   GRPC_INITIAL_METADATA_WAIT_FOR_READY |                \
+   GRPC_INITIAL_METADATA_CACHEABLE_REQUEST |             \
+   GRPC_INITIAL_METADATA_WAIT_FOR_READY_EXPLICITLY_SET | \
+   GRPC_INITIAL_METADATA_CORKED)
 
 /** A single metadata element */
 typedef struct grpc_metadata {

src/core/ext/transport/chttp2/transport/chttp2_transport.c

@@ -1210,8 +1210,13 @@ static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx, void *stream_op,
           }
         } else {
           GPR_ASSERT(s->id != 0);
-          grpc_chttp2_become_writable(exec_ctx, t, s,
-                                      GRPC_CHTTP2_STREAM_WRITE_INITIATE_COVERED,
+          grpc_chttp2_stream_write_type write_type =
+              GRPC_CHTTP2_STREAM_WRITE_INITIATE_COVERED;
+          if (op->send_message != NULL &&
+              (op->send_message->flags & GRPC_WRITE_BUFFER_HINT)) {
+            write_type = GRPC_CHTTP2_STREAM_WRITE_PIGGYBACK;
+          }
+          grpc_chttp2_become_writable(exec_ctx, t, s, write_type,
                                       "op.send_initial_metadata");
         }
       } else {

src/cpp/client/client_context.cc

@@ -67,7 +67,8 @@ ClientContext::ClientContext()
       call_canceled_(false),
       deadline_(gpr_inf_future(GPR_CLOCK_REALTIME)),
       census_context_(nullptr),
-      propagate_from_call_(nullptr) {
+      propagate_from_call_(nullptr),
+      initial_metadata_corked_(false) {
   g_client_callbacks->DefaultConstructor(this);
 }
 

src/objective-c/GRPCClient/GRPCCall.m

@@ -36,6 +36,7 @@
 #include <grpc/grpc.h>
 #include <grpc/support/time.h>
 #import <RxLibrary/GRXConcurrentWriteable.h>
+#import <RxLibrary/GRXImmediateSingleWriter.h>
 
 #import "private/GRPCConnectivityMonitor.h"
 #import "private/GRPCHost.h"
@@ -45,6 +46,11 @@
 #import "private/NSDictionary+GRPC.h"
 #import "private/NSError+GRPC.h"
 
+// At most 6 ops can be in an op batch for a client: SEND_INITIAL_METADATA,
+// SEND_MESSAGE, SEND_CLOSE_FROM_CLIENT, RECV_INITIAL_METADATA, RECV_MESSAGE,
+// and RECV_STATUS_ON_CLIENT.
+NSInteger kMaxClientBatch = 6;
+
 NSString * const kGRPCHeadersKey = @"io.grpc.HeadersKey";
 NSString * const kGRPCTrailersKey = @"io.grpc.TrailersKey";
 static NSMutableDictionary *callFlags;
@@ -100,6 +106,13 @@ static NSMutableDictionary *callFlags;
   GRPCCall *_retainSelf;
 
   GRPCRequestHeaders *_requestHeaders;
+
+  // In the case that the call is a unary call (i.e. the writer to GRPCCall is of type
+  // GRXImmediateSingleWriter), GRPCCall will delay sending ops (not send them to C core
+  // immediately) and buffer them into a batch _unaryOpBatch. The batch is sent to C core when
+  // the SendClose op is added.
+  BOOL _unaryCall;
+  NSMutableArray *_unaryOpBatch;
 }
 
 @synthesize state = _state;
@@ -157,6 +170,11 @@ static NSMutableDictionary *callFlags;
     _requestWriter = requestWriter;
 
     _requestHeaders = [[GRPCRequestHeaders alloc] initWithCall:self];
+
+    if ([requestWriter isKindOfClass:[GRXImmediateSingleWriter class]]) {
+      _unaryCall = YES;
+      _unaryOpBatch = [NSMutableArray arrayWithCapacity:kMaxClientBatch];
+    }
   }
   return self;
 }
@@ -165,6 +183,9 @@ static NSMutableDictionary *callFlags;
 
 - (void)finishWithError:(NSError *)errorOrNil {
   @synchronized(self) {
+    if (_state == GRXWriterStateFinished) {
+      return;
+    }
     _state = GRXWriterStateFinished;
   }
 
@@ -254,15 +275,22 @@ static NSMutableDictionary *callFlags;
 
 - (void)sendHeaders:(NSDictionary *)headers {
   // TODO(jcanizales): Add error handlers for async failures
-  [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendMetadata alloc] initWithMetadata:headers
-                                                                                  flags:[GRPCCall callFlagsForHost:_host path:_path]
-                                                                                handler:nil]]];
+  GRPCOpSendMetadata *op = [[GRPCOpSendMetadata alloc] initWithMetadata:headers
+                                                                  flags:[GRPCCall callFlagsForHost:_host path:_path]
+                                                                handler:nil];  // No clean-up needed after SEND_INITIAL_METADATA
+  if (!_unaryCall) {
+    [_wrappedCall startBatchWithOperations:@[op]];
+  } else {
+    [_unaryOpBatch addObject:op];
+  }
 }
 
 #pragma mark GRXWriteable implementation
 
 // Only called from the call queue. The error handler will be called from the
 // network queue if the write didn't succeed.
+// If the call is a unary call, parameter \a errorHandler will be ignored and
+// the error handler of GRPCOpSendClose will be executed in case of error.
 - (void)writeMessage:(NSData *)message withErrorHandler:(void (^)())errorHandler {
 
   __weak GRPCCall *weakSelf = self;
@@ -275,9 +303,17 @@ static NSMutableDictionary *callFlags;
       }
     }
   };
-  [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendMessage alloc] initWithMessage:message
-                                                                              handler:resumingHandler]]
-                            errorHandler:errorHandler];
+
+  GRPCOpSendMessage *op = [[GRPCOpSendMessage alloc] initWithMessage:message
+                                                             handler:resumingHandler];
+  if (!_unaryCall) {
+    [_wrappedCall startBatchWithOperations:@[op]
+                              errorHandler:errorHandler];
+  } else {
+    // Ignored errorHandler since it is the same as the one for GRPCOpSendClose.
+    // TODO (mxyan): unify the error handlers of all Ops into a single closure.
+    [_unaryOpBatch addObject:op];
+  }
 }
 
 - (void)writeValue:(id)value {
@@ -302,8 +338,14 @@ static NSMutableDictionary *callFlags;
 // Only called from the call queue. The error handler will be called from the
 // network queue if the requests stream couldn't be closed successfully.
 - (void)finishRequestWithErrorHandler:(void (^)())errorHandler {
-  [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendClose alloc] init]]
-                            errorHandler:errorHandler];
+  if (!_unaryCall) {
+    [_wrappedCall startBatchWithOperations:@[[[GRPCOpSendClose alloc] init]]
+                              errorHandler:errorHandler];
+  } else {
+    [_unaryOpBatch addObject:[[GRPCOpSendClose alloc] init]];
+    [_wrappedCall startBatchWithOperations:_unaryOpBatch
+                              errorHandler:errorHandler];
+  }
 }
 
 - (void)writesFinishedWithError:(NSError *)errorOrNil {

src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.h

@@ -0,0 +1,61 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifdef GRPC_TEST_OBJC
+
+#import "../GRPCCall.h"
+
+/**
+ * Methods used for gRPC internal tests. DO NOT USE.
+ */
+@interface GRPCCall (InternalTests)
+
+/**
+ * Enables logging of op batches. Memory consumption increases as more ops are logged.
+ *
+ * This function is for internal testing of gRPC only. It is not part of gRPC's public interface.
+ * Do not use in production. To enable, set the preprocessor flag GRPC_TEST_OBJC.
+ */
++ (void)enableOpBatchLog:(BOOL)enabled;
+
+/**
+ * Obtain the logged op batches. Invoking this method will clean the log.
+ *
+ * This function is for internal testing of gRPC only. It is not part of gRPC's public interface.
+ * Do not use in production. To enable, set the preprocessor flag GRPC_TEST_OBJC.
+ */
++ (NSArray *)obtainAndCleanOpBatchLog;
+
+@end
+
+#endif

src/objective-c/GRPCClient/internal_testing/GRPCCall+InternalTests.m

@@ -0,0 +1,52 @@
+/*
+ *
+ * Copyright 2017, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifdef GRPC_TEST_OBJC
+
+#import "GRPCCall+InternalTests.h"
+
+#import "../private/GRPCOpBatchLog.h"
+
+@implementation GRPCCall (InternalTests)
+
++ (void)enableOpBatchLog:(BOOL)enabled {
+  [GRPCOpBatchLog enableOpBatchLog:enabled];
+}
+
++ (NSArray *)obtainAndCleanOpBatchLog {
+  return [GRPCOpBatchLog obtainAndCleanOpBatchLog];
+}
+
+@end
+
+#endif

src/objective-c/GRPCClient/private/GRPCOpBatchLog.h

@@ -0,0 +1,59 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+
+#ifdef GRPC_TEST_OBJC
+
+/**
+ * Logs the op batches of a client. Used for testing.
+ */
+@interface GRPCOpBatchLog : NSObject
+
+/**
+ * Enables logging of op batches. Memory consumption increases as more ops are logged.
+ */
++ (void)enableOpBatchLog:(BOOL)enabled;
+
+/**
+ * Add an op batch to log.
+ */
++ (void)addOpBatchToLog:(NSArray *)batch;
+
+/**
+ * Obtain the logged op batches. Invoking this method will clean the log.
+ */
++ (NSArray *)obtainAndCleanOpBatchLog;
+
+@end
+
+#endif

src/objective-c/GRPCClient/private/GRPCOpBatchLog.m

@@ -0,0 +1,72 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifdef GRPC_TEST_OBJC
+
+#import "GRPCOpBatchLog.h"
+
+static NSMutableArray *opBatchLog = nil;
+
+@implementation GRPCOpBatchLog
+
++ (void)enableOpBatchLog:(BOOL)enabled {
+  @synchronized (opBatchLog) {
+    if (enabled) {
+      if (!opBatchLog) {
+        opBatchLog = [NSMutableArray array];
+      }
+    } else {
+      if (opBatchLog) {
+        opBatchLog = nil;
+      }
+    }
+  }
+}
+
++ (void)addOpBatchToLog:(NSArray *)batch {
+  @synchronized (opBatchLog) {
+    [opBatchLog addObject:batch];
+  }
+}
+
++ (NSArray *)obtainAndCleanOpBatchLog {
+  @synchronized (opBatchLog) {
+    NSArray *out = opBatchLog;
+    opBatchLog = [NSMutableArray array];
+    return out;
+  }
+}
+
+@end
+
+#endif

src/objective-c/GRPCClient/private/GRPCWrappedCall.m

@@ -44,6 +44,8 @@
 #import "NSData+GRPC.h"
 #import "NSError+GRPC.h"
 
+#import "GRPCOpBatchLog.h"
+
 @implementation GRPCOperation {
 @protected
   // Most operation subclasses don't set any flags in the grpc_op, and rely on the flag member being
@@ -274,6 +276,12 @@
 }
 
 - (void)startBatchWithOperations:(NSArray *)operations errorHandler:(void (^)())errorHandler {
+  // Keep logs of op batches when we are running tests. Disabled when in production for improved
+  // performance.
+#ifdef GRPC_TEST_OBJC
+  [GRPCOpBatchLog addOpBatchToLog:operations];
+#endif
+
   size_t nops = operations.count;
   grpc_op *ops_array = gpr_malloc(nops * sizeof(grpc_op));
   size_t i = 0;

src/objective-c/RxLibrary/GRXImmediateSingleWriter.h

@@ -0,0 +1,50 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#import <Foundation/Foundation.h>
+
+#import "GRXImmediateWriter.h"
+
+/**
+ * Utility to construct GRXWriter instances from values that are immediately available when
+ * required.
+ */
+@interface GRXImmediateSingleWriter : GRXImmediateWriter
+
+/**
+ * Returns a writer that sends the passed value to its writeable and then finishes (releasing the
+ * value).
+ */
++ (GRXWriter *)writerWithValue:(id)value;
+
+@end

src/objective-c/RxLibrary/GRXImmediateSingleWriter.m

@@ -0,0 +1,89 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#import "GRXImmediateSingleWriter.h"
+
+@implementation GRXImmediateSingleWriter {
+  id _value;
+  id<GRXWriteable> _writeable;
+}
+
+@synthesize state = _state;
+
+- (instancetype)initWithValue:(id)value {
+  if (self = [super init]) {
+    _value = value;
+    _state = GRXWriterStateNotStarted;
+  }
+  return self;
+}
+
++ (GRXWriter *)writerWithValue:(id)value {
+  return [[self alloc] initWithValue:value];
+}
+
+- (void)startWithWriteable:(id<GRXWriteable>)writeable {
+  _state = GRXWriterStateStarted;
+  _writeable = writeable;
+  [writeable writeValue:_value];
+  [self finish];
+}
+
+- (void)finish {
+  _state = GRXWriterStateFinished;
+  _value = nil;
+  id<GRXWriteable> writeable = _writeable;
+  _writeable = nil;
+  [writeable writesFinishedWithError:nil];
+}
+
+// Overwrite the setter to disallow manual state transition. The getter
+// of _state is synthesized.
+- (void)setState:(GRXWriterState)newState {
+  // Manual state transition is not allowed
+  return;
+}
+
+// Overrides [requestWriter(Transformations):map:] for Protocol Buffers
+// encoding.
+// We need the return value of this map to be a GRXImmediateSingleWriter but
+// the original \a map function returns a new Writer of another type. So we
+// need to override this function here.
+- (GRXWriter *)map:(id (^)(id))map {
+  // Since _value is available when creating the object, we can simply
+  // apply the map and store the output.
+  _value = map(_value);
+  return self;
+}
+
+@end

src/objective-c/RxLibrary/GRXWriter+Immediate.m

@@ -34,6 +34,7 @@
 #import "GRXWriter+Immediate.h"
 
 #import "GRXImmediateWriter.h"
+#import "GRXImmediateSingleWriter.h"
 
 @implementation GRXWriter (Immediate)
 
@@ -50,7 +51,7 @@
 }
 
 + (instancetype)writerWithValue:(id)value {
-  return [GRXImmediateWriter writerWithValue:value];
+  return [GRXImmediateSingleWriter writerWithValue:value];
 }
 
 + (instancetype)writerWithError:(NSError *)error {

src/objective-c/tests/GRPCClientTests.m

@@ -38,6 +38,7 @@
 #import <GRPCClient/GRPCCall+ChannelArg.h>
 #import <GRPCClient/GRPCCall+OAuth2.h>
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 #import <ProtoRPC/ProtoMethod.h>
 #import <RemoteTest/Messages.pbobjc.h>
 #import <RxLibrary/GRXWriteable.h>

src/objective-c/tests/InteropTests.m

@@ -38,6 +38,7 @@
 #import <Cronet/Cronet.h>
 #import <GRPCClient/GRPCCall+ChannelArg.h>
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 #import <GRPCClient/GRPCCall+Cronet.h>
 #import <ProtoRPC/ProtoRPC.h>
 #import <RemoteTest/Messages.pbobjc.h>
@@ -45,6 +46,8 @@
 #import <RemoteTest/Test.pbrpc.h>
 #import <RxLibrary/GRXBufferedPipe.h>
 #import <RxLibrary/GRXWriter+Immediate.h>
+#import <grpc/support/log.h>
+#import <grpc/grpc.h>
 
 #define TEST_TIMEOUT 32
 
@@ -97,15 +100,6 @@
   return 0;
 }
 
-+ (void)setUp {
-#ifdef GRPC_COMPILE_WITH_CRONET
-  // Cronet setup
-  [Cronet setHttp2Enabled:YES];
-  [Cronet start];
-  [GRPCCall useCronetWithEngine:[Cronet getGlobalEngine]];
-#endif
-}
-
 - (void)setUp {
   self.continueAfterFailure = NO;
 
@@ -155,6 +149,44 @@
   [self waitForExpectationsWithTimeout:TEST_TIMEOUT handler:nil];
 }
 
+- (void)testPacketCoalescing {
+  XCTAssertNotNil(self.class.host);
+  __weak XCTestExpectation *expectation = [self expectationWithDescription:@"LargeUnary"];
+
+  RMTSimpleRequest *request = [RMTSimpleRequest message];
+  request.responseType = RMTPayloadType_Compressable;
+  request.responseSize = 10;
+  request.payload.body = [NSMutableData dataWithLength:10];
+
+  [GRPCCall enableOpBatchLog:YES];
+  [_service unaryCallWithRequest:request handler:^(RMTSimpleResponse *response, NSError *error) {
+    XCTAssertNil(error, @"Finished with unexpected error: %@", error);
+
+    RMTSimpleResponse *expectedResponse = [RMTSimpleResponse message];
+    expectedResponse.payload.type = RMTPayloadType_Compressable;
+    expectedResponse.payload.body = [NSMutableData dataWithLength:10];
+    XCTAssertEqualObjects(response, expectedResponse);
+
+    // The test is a success if there is a batch of exactly 3 ops (SEND_INITIAL_METADATA,
+    // SEND_MESSAGE, SEND_CLOSE_FROM_CLIENT). Without packet coalescing each batch of ops contains
+    // only one op.
+    NSArray *opBatches = [GRPCCall obtainAndCleanOpBatchLog];
+    const NSInteger kExpectedOpBatchSize = 3;
+    for (NSObject *o in opBatches) {
+      if ([o isKindOfClass:[NSArray class]]) {
+        NSArray *batch = (NSArray *)o;
+        if ([batch count] == kExpectedOpBatchSize) {
+          [expectation fulfill];
+          break;
+        }
+      }
+    }
+  }];
+
+  [self waitForExpectationsWithTimeout:16 handler:nil];
+  [GRPCCall enableOpBatchLog:NO];
+}
+
 - (void)test4MBResponsesAreAccepted {
   XCTAssertNotNil(self.class.host);
   __weak XCTestExpectation *expectation = [self expectationWithDescription:@"MaxResponseSize"];

src/objective-c/tests/InteropTestsLocalCleartext.m

@@ -32,6 +32,7 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 
 #import "InteropTests.h"
 

src/objective-c/tests/InteropTestsLocalSSL.m

@@ -32,6 +32,7 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 
 #import "InteropTests.h"
 

src/objective-c/tests/InteropTestsRemote.m

@@ -32,6 +32,7 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
 
 #import "InteropTests.h"
 

src/objective-c/tests/InteropTestsRemoteWithCronet/InteropTestsRemoteWithCronet.m

@@ -32,6 +32,10 @@
  */
 
 #import <GRPCClient/GRPCCall+Tests.h>
+#import <GRPCClient/internal_testing/GRPCCall+InternalTests.h>
+
+#import <Cronet/Cronet.h>
+#import <GRPCClient/GRPCCall+Cronet.h>
 
 #import "InteropTests.h"
 

src/objective-c/tests/Podfile

@@ -97,15 +97,20 @@ post_install do |installer|
         # GPR_UNREACHABLE_CODE causes "Control may reach end of non-void
         # function" warning
         config.build_settings['GCC_WARN_ABOUT_RETURN_TYPE'] = 'NO'
+        config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_CRONET_WITH_PACKET_COALESCING=1'
       end
     end
 
     # Activate Cronet for the dedicated build configuration 'Cronet', which will be used solely by
     # the test target 'InteropTestsRemoteWithCronet'
+    # Activate GRPCCall+InternalTests functions for the dedicated build configuration 'Test', which will
+    # be used by all test targets using it.
     if target.name == 'gRPC'
       target.build_configurations.each do |config|
         if config.name == 'Cronet'
-          config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_COMPILE_WITH_CRONET=1'
+          config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_COMPILE_WITH_CRONET=1 GRPC_TEST_OBJC=1'
+        elsif config.name == 'Test'
+          config.build_settings['GCC_PREPROCESSOR_DEFINITIONS'] = '$(inherited) COCOAPODS=1 GRPC_TEST_OBJC=1'
         end
       end
     end

src/objective-c/tests/Tests.xcodeproj/project.pbxproj

@@ -125,8 +125,10 @@
 		0A4F89D9C90E9C30990218F0 /* Pods.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = Pods.release.xcconfig; path = "Pods/Target Support Files/Pods/Pods.release.xcconfig"; sourceTree = "<group>"; };
 		0D2284C3DF7E57F0ED504E39 /* Pods-CoreCronetEnd2EndTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CoreCronetEnd2EndTests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-CoreCronetEnd2EndTests/Pods-CoreCronetEnd2EndTests.debug.xcconfig"; sourceTree = "<group>"; };
 		14B09A58FEE53A7A6B838920 /* Pods-InteropTestsLocalSSL.cronet.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsLocalSSL.cronet.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsLocalSSL/Pods-InteropTestsLocalSSL.cronet.xcconfig"; sourceTree = "<group>"; };
+		1588C85DEAF7FC0ACDEA4C02 /* Pods-InteropTestsLocalCleartext.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsLocalCleartext.test.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsLocalCleartext/Pods-InteropTestsLocalCleartext.test.xcconfig"; sourceTree = "<group>"; };
 		17F60BF2871F6AF85FB3FA12 /* Pods-InteropTestsRemoteWithCronet.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsRemoteWithCronet.debug.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsRemoteWithCronet/Pods-InteropTestsRemoteWithCronet.debug.xcconfig"; sourceTree = "<group>"; };
 		20DFF2F3C97EF098FE5A3171 /* libPods-Tests.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = "libPods-Tests.a"; sourceTree = BUILT_PRODUCTS_DIR; };
+		2B89F3037963E6EDDD48D8C3 /* Pods-InteropTestsRemoteWithCronet.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsRemoteWithCronet.test.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsRemoteWithCronet/Pods-InteropTestsRemoteWithCronet.test.xcconfig"; sourceTree = "<group>"; };
 		35F2B6BF3BAE8F0DC4AFD76E /* libPods.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = libPods.a; sourceTree = BUILT_PRODUCTS_DIR; };
 		386712AEACF7C2190C4B8B3F /* Pods-CronetUnitTests.cronet.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CronetUnitTests.cronet.xcconfig"; path = "Pods/Target Support Files/Pods-CronetUnitTests/Pods-CronetUnitTests.cronet.xcconfig"; sourceTree = "<group>"; };
 		3B0861FC805389C52DB260D4 /* Pods-RxLibraryUnitTests.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-RxLibraryUnitTests.release.xcconfig"; path = "Pods/Target Support Files/Pods-RxLibraryUnitTests/Pods-RxLibraryUnitTests.release.xcconfig"; sourceTree = "<group>"; };
@@ -162,15 +164,22 @@
 		63E240CD1B6C4E2B005F3B0E /* InteropTestsLocalSSL.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = InteropTestsLocalSSL.m; sourceTree = "<group>"; };
 		63E240CF1B6C63DC005F3B0E /* TestCertificates.bundle */ = {isa = PBXFileReference; lastKnownFileType = "wrapper.plug-in"; path = TestCertificates.bundle; sourceTree = "<group>"; };
 		64F68A9A6A63CC930DD30A6E /* Pods-CronetUnitTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CronetUnitTests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-CronetUnitTests/Pods-CronetUnitTests.debug.xcconfig"; sourceTree = "<group>"; };
+		6793C9D019CB268C5BB491A2 /* Pods-CoreCronetEnd2EndTests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CoreCronetEnd2EndTests.test.xcconfig"; path = "Pods/Target Support Files/Pods-CoreCronetEnd2EndTests/Pods-CoreCronetEnd2EndTests.test.xcconfig"; sourceTree = "<group>"; };
+		781089FAE980F51F88A3BE0B /* Pods-RxLibraryUnitTests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-RxLibraryUnitTests.test.xcconfig"; path = "Pods/Target Support Files/Pods-RxLibraryUnitTests/Pods-RxLibraryUnitTests.test.xcconfig"; sourceTree = "<group>"; };
 		79C68EFFCB5533475D810B79 /* Pods-RxLibraryUnitTests.cronet.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-RxLibraryUnitTests.cronet.xcconfig"; path = "Pods/Target Support Files/Pods-RxLibraryUnitTests/Pods-RxLibraryUnitTests.cronet.xcconfig"; sourceTree = "<group>"; };
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+		A0361771A855917162911180 /* Pods-Tests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Tests.test.xcconfig"; path = "Pods/Target Support Files/Pods-Tests/Pods-Tests.test.xcconfig"; sourceTree = "<group>"; };
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+		B226619DC4E709E0FFFF94B8 /* Pods-CronetUnitTests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-CronetUnitTests.test.xcconfig"; path = "Pods/Target Support Files/Pods-CronetUnitTests/Pods-CronetUnitTests.test.xcconfig"; sourceTree = "<group>"; };
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+		D13BEC8181B8E678A1B52F54 /* Pods-InteropTestsLocalSSL.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-InteropTestsLocalSSL.test.xcconfig"; path = "Pods/Target Support Files/Pods-InteropTestsLocalSSL/Pods-InteropTestsLocalSSL.test.xcconfig"; sourceTree = "<group>"; };
+		DB1F4391AF69D20D38D74B67 /* Pods-AllTests.test.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-AllTests.test.xcconfig"; path = "Pods/Target Support Files/Pods-AllTests/Pods-AllTests.test.xcconfig"; sourceTree = "<group>"; };
 		DBE059B4AC7A51919467EEC0 /* libPods-InteropTestsRemote.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = "libPods-InteropTestsRemote.a"; sourceTree = BUILT_PRODUCTS_DIR; };
 		DBEDE45BDA60DF1E1C8950C0 /* libPods-InteropTestsLocalSSL.a */ = {isa = PBXFileReference; explicitFileType = archive.ar; includeInIndex = 0; path = "libPods-InteropTestsLocalSSL.a"; sourceTree = BUILT_PRODUCTS_DIR; };
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@@ -317,6 +326,15 @@
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 				02192CF1FF9534E3D18C65FC /* Pods-CronetUnitTests.release.xcconfig */,
+				DB1F4391AF69D20D38D74B67 /* Pods-AllTests.test.xcconfig */,
+				6793C9D019CB268C5BB491A2 /* Pods-CoreCronetEnd2EndTests.test.xcconfig */,
+				B226619DC4E709E0FFFF94B8 /* Pods-CronetUnitTests.test.xcconfig */,
+				1588C85DEAF7FC0ACDEA4C02 /* Pods-InteropTestsLocalCleartext.test.xcconfig */,
+				D13BEC8181B8E678A1B52F54 /* Pods-InteropTestsLocalSSL.test.xcconfig */,
+				A6F832FCEFA6F6881E620F12 /* Pods-InteropTestsRemote.test.xcconfig */,
+				2B89F3037963E6EDDD48D8C3 /* Pods-InteropTestsRemoteWithCronet.test.xcconfig */,
+				781089FAE980F51F88A3BE0B /* Pods-RxLibraryUnitTests.test.xcconfig */,
+				A0361771A855917162911180 /* Pods-Tests.test.xcconfig */,
 			);
 			name = Pods;
 			sourceTree = "<group>";
@@ -1237,6 +1255,210 @@
 /* End PBXTargetDependency section */
 
 /* Begin XCBuildConfiguration section */
+		5E1228981E4D400F00E8504F /* Test */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				ALWAYS_SEARCH_USER_PATHS = NO;
+				CLANG_CXX_LANGUAGE_STANDARD = "gnu++0x";
+				CLANG_CXX_LIBRARY = "libc++";
+				CLANG_ENABLE_MODULES = YES;
+				CLANG_ENABLE_OBJC_ARC = YES;
+				CLANG_WARN_BOOL_CONVERSION = YES;
+				CLANG_WARN_CONSTANT_CONVERSION = YES;
+				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
+				CLANG_WARN_EMPTY_BODY = YES;
+				CLANG_WARN_ENUM_CONVERSION = YES;
+				CLANG_WARN_INT_CONVERSION = YES;
+				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
+				CLANG_WARN_UNREACHABLE_CODE = YES;
+				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
+				COPY_PHASE_STRIP = NO;
+				DEBUG_INFORMATION_FORMAT = "dwarf-with-dsym";
+				ENABLE_STRICT_OBJC_MSGSEND = YES;
+				GCC_C_LANGUAGE_STANDARD = gnu99;
+				GCC_DYNAMIC_NO_PIC = NO;
+				GCC_NO_COMMON_BLOCKS = YES;
+				GCC_OPTIMIZATION_LEVEL = 0;
+				GCC_PREPROCESSOR_DEFINITIONS = (
+					"DEBUG=1",
+					"$(inherited)",
+				);
+				GCC_SYMBOLS_PRIVATE_EXTERN = NO;
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
+				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
+				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
+				GCC_WARN_UNDECLARED_SELECTOR = YES;
+				GCC_WARN_UNINITIALIZED_AUTOS = YES_AGGRESSIVE;
+				GCC_WARN_UNUSED_FUNCTION = YES;
+				GCC_WARN_UNUSED_VARIABLE = YES;
+				IPHONEOS_DEPLOYMENT_TARGET = 8.3;
+				MTL_ENABLE_DEBUG_INFO = YES;
+				ONLY_ACTIVE_ARCH = YES;
+				SDKROOT = iphoneos;
+			};
+			name = Test;
+		};
+		5E1228991E4D400F00E8504F /* Test */ = {
+			isa = XCBuildConfiguration;
+			baseConfigurationReference = A0361771A855917162911180 /* Pods-Tests.test.xcconfig */;
+			buildSettings = {
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
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+			name = Test;
+		};
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+			buildSettings = {
+				FRAMEWORK_SEARCH_PATHS = (
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+				);
+				GCC_PREPROCESSOR_DEFINITIONS = (
+					"DEBUG=1",
+					"$(inherited)",
+					"GRPC_TEST_OBJC=1",
+				);
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+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_NAME = "$(TARGET_NAME)";
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+			name = Test;
+		};
+		5E12289B1E4D400F00E8504F /* Test */ = {
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+			buildSettings = {
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+				ENABLE_TESTABILITY = YES;
+				INFOPLIST_FILE = Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.RxLibraryUnitTests;
+				PRODUCT_NAME = "$(TARGET_NAME)";
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+			name = Test;
+		};
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+			buildSettings = {
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+				ENABLE_TESTABILITY = YES;
+				GCC_PREPROCESSOR_DEFINITIONS = (
+					"$(inherited)",
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+					"$(inherited)",
+					"GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1",
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+				);
+				INFOPLIST_FILE = Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.InteropTests;
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+				);
+				INFOPLIST_FILE = Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.InteropTestsLocalSSL;
+				PRODUCT_NAME = "$(TARGET_NAME)";
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+		5E12289E1E4D400F00E8504F /* Test */ = {
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+					"GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1",
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+				);
+				INFOPLIST_FILE = Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.InteropTestsLocalCleartext;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+			};
+			name = Test;
+		};
+		5E12289F1E4D400F00E8504F /* Test */ = {
+			isa = XCBuildConfiguration;
+			baseConfigurationReference = 6793C9D019CB268C5BB491A2 /* Pods-CoreCronetEnd2EndTests.test.xcconfig */;
+			buildSettings = {
+				CLANG_ANALYZER_NONNULL = YES;
+				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "iPhone Developer";
+				DEBUG_INFORMATION_FORMAT = dwarf;
+				ENABLE_TESTABILITY = YES;
+				INFOPLIST_FILE = CoreCronetEnd2EndTests/Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.3;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.CoreCronetEnd2EndTests;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				USER_HEADER_SEARCH_PATHS = "$(inherited) \"${PODS_ROOT}/../../../..\"";
+			};
+			name = Test;
+		};
+		5E1228A01E4D400F00E8504F /* Test */ = {
+			isa = XCBuildConfiguration;
+			baseConfigurationReference = 2B89F3037963E6EDDD48D8C3 /* Pods-InteropTestsRemoteWithCronet.test.xcconfig */;
+			buildSettings = {
+				CLANG_ANALYZER_NONNULL = YES;
+				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "iPhone Developer";
+				DEBUG_INFORMATION_FORMAT = dwarf;
+				ENABLE_TESTABILITY = YES;
+				GCC_PREPROCESSOR_DEFINITIONS = (
+					"$(inherited)",
+					"COCOAPODS=1",
+					"GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1",
+					"GRPC_TEST_OBJC=1",
+				);
+				INFOPLIST_FILE = InteropTestsRemoteWithCronet/Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.3;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.InteropTestsRemoteWithCronet;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+			};
+			name = Test;
+		};
+		5E1228A11E4D400F00E8504F /* Test */ = {
+			isa = XCBuildConfiguration;
+			baseConfigurationReference = B226619DC4E709E0FFFF94B8 /* Pods-CronetUnitTests.test.xcconfig */;
+			buildSettings = {
+				CLANG_ANALYZER_NONNULL = YES;
+				"CODE_SIGN_IDENTITY[sdk=iphoneos*]" = "iPhone Developer";
+				DEBUG_INFORMATION_FORMAT = dwarf;
+				ENABLE_TESTABILITY = YES;
+				INFOPLIST_FILE = CronetUnitTests/Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 9.3;
+				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
+				PRODUCT_BUNDLE_IDENTIFIER = io.grpc.CronetUnitTests;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				USER_HEADER_SEARCH_PATHS = "\"${PODS_ROOT}/../../../..\" $(inherited)";
+			};
+			name = Test;
+		};
 		5E8A5DAC1D3840B4000F8BC4 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			baseConfigurationReference = 0D2284C3DF7E57F0ED504E39 /* Pods-CoreCronetEnd2EndTests.debug.xcconfig */;
@@ -1407,6 +1629,12 @@
 			buildSettings = {
 				DEBUG_INFORMATION_FORMAT = dwarf;
 				ENABLE_TESTABILITY = YES;
+				GCC_PREPROCESSOR_DEFINITIONS = (
+					"$(inherited)",
+					"COCOAPODS=1",
+					"$(inherited)",
+					"GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1",
+				);
 				INFOPLIST_FILE = Info.plist;
 				IPHONEOS_DEPLOYMENT_TARGET = 9.0;
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
@@ -1471,10 +1699,10 @@
 				GCC_PREPROCESSOR_DEFINITIONS = (
 					"$(inherited)",
 					"COCOAPODS=1",
-					"$(inherited)",
 					"GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1",
 					"GRPC_COMPILE_WITH_CRONET=1",
 					"GRPC_CRONET_WITH_PACKET_COALESCING=1",
+					"GRPC_TEST_OBJC=1",
 				);
 				INFOPLIST_FILE = InteropTestsRemoteWithCronet/Info.plist;
 				IPHONEOS_DEPLOYMENT_TARGET = 9.3;
@@ -1495,7 +1723,6 @@
 				GCC_PREPROCESSOR_DEFINITIONS = (
 					"$(inherited)",
 					"COCOAPODS=1",
-					"$(inherited)",
 					"GPB_USE_PROTOBUF_FRAMEWORK_IMPORTS=1",
 				);
 				INFOPLIST_FILE = InteropTestsRemoteWithCronet/Info.plist;
@@ -1770,6 +1997,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				5E8A5DAC1D3840B4000F8BC4 /* Debug */,
+				5E12289F1E4D400F00E8504F /* Test */,
 				5EC3C7A71D4FC18C000330E2 /* Cronet */,
 				5E8A5DAD1D3840B4000F8BC4 /* Release */,
 			);
@@ -1780,6 +2008,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				5EAD6D2C1E27047400002378 /* Debug */,
+				5E1228A11E4D400F00E8504F /* Test */,
 				5EAD6D2D1E27047400002378 /* Cronet */,
 				5EAD6D2E1E27047400002378 /* Release */,
 			);
@@ -1790,6 +2019,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				5EE84BF91D4717E40050C6CC /* Debug */,
+				5E1228A01E4D400F00E8504F /* Test */,
 				5EC3C7A81D4FC18C000330E2 /* Cronet */,
 				5EE84BFA1D4717E40050C6CC /* Release */,
 			);
@@ -1800,6 +2030,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				63423F4E1B150A5F006CF63C /* Debug */,
+				5E12289A1E4D400F00E8504F /* Test */,
 				5EC3C7A21D4FC18C000330E2 /* Cronet */,
 				63423F4F1B150A5F006CF63C /* Release */,
 			);
@@ -1810,6 +2041,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				635697D91B14FC11007A7283 /* Debug */,
+				5E1228981E4D400F00E8504F /* Test */,
 				5EC3C7A01D4FC18C000330E2 /* Cronet */,
 				635697DA1B14FC11007A7283 /* Release */,
 			);
@@ -1820,6 +2052,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				635697DC1B14FC11007A7283 /* Debug */,
+				5E1228991E4D400F00E8504F /* Test */,
 				5EC3C7A11D4FC18C000330E2 /* Cronet */,
 				635697DD1B14FC11007A7283 /* Release */,
 			);
@@ -1830,6 +2063,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				63DC841C1BE15179000708E8 /* Debug */,
+				5E12289B1E4D400F00E8504F /* Test */,
 				5EC3C7A31D4FC18C000330E2 /* Cronet */,
 				63DC841D1BE15179000708E8 /* Release */,
 			);
@@ -1840,6 +2074,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				63DC842C1BE15267000708E8 /* Debug */,
+				5E12289C1E4D400F00E8504F /* Test */,
 				5EC3C7A41D4FC18C000330E2 /* Cronet */,
 				63DC842D1BE15267000708E8 /* Release */,
 			);
@@ -1850,6 +2085,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				63DC843D1BE15294000708E8 /* Debug */,
+				5E12289D1E4D400F00E8504F /* Test */,
 				5EC3C7A51D4FC18C000330E2 /* Cronet */,
 				63DC843E1BE15294000708E8 /* Release */,
 			);
@@ -1860,6 +2096,7 @@
 			isa = XCConfigurationList;
 			buildConfigurations = (
 				63DC844C1BE152B5000708E8 /* Debug */,
+				5E12289E1E4D400F00E8504F /* Test */,
 				5EC3C7A61D4FC18C000330E2 /* Cronet */,
 				63DC844D1BE152B5000708E8 /* Release */,
 			);

src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/AllTests.xcscheme

@@ -23,7 +23,7 @@
       </BuildActionEntries>
    </BuildAction>
    <TestAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -63,7 +63,7 @@
       </AdditionalOptions>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
@@ -101,7 +101,7 @@
       </MacroExpansion>
    </ProfileAction>
    <AnalyzeAction
-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
    </AnalyzeAction>
    <ArchiveAction
       buildConfiguration = "Release"

src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalCleartext.xcscheme

@@ -23,7 +23,7 @@
       </BuildActionEntries>
    </BuildAction>
    <TestAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -54,7 +54,7 @@
       </AdditionalOptions>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
@@ -92,7 +92,7 @@
       </MacroExpansion>
    </ProfileAction>
    <AnalyzeAction
-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
    </AnalyzeAction>
    <ArchiveAction
       buildConfiguration = "Release"

src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsLocalSSL.xcscheme

@@ -23,7 +23,7 @@
       </BuildActionEntries>
    </BuildAction>
    <TestAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -57,7 +57,7 @@
       </AdditionalOptions>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
@@ -86,7 +86,7 @@
       debugDocumentVersioning = "YES">
    </ProfileAction>
    <AnalyzeAction
-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
    </AnalyzeAction>
    <ArchiveAction
       buildConfiguration = "Release"

src/objective-c/tests/Tests.xcodeproj/xcshareddata/xcschemes/InteropTestsRemote.xcscheme

@@ -23,7 +23,7 @@
       </BuildActionEntries>
    </BuildAction>
    <TestAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">
@@ -57,7 +57,7 @@
       </AdditionalOptions>
    </TestAction>
    <LaunchAction
-      buildConfiguration = "Debug"
+      buildConfiguration = "Test"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       launchStyle = "0"
@@ -86,7 +86,7 @@
       debugDocumentVersioning = "YES">
    </ProfileAction>
    <AnalyzeAction
-      buildConfiguration = "Debug">
+      buildConfiguration = "Test">
    </AnalyzeAction>
    <ArchiveAction
       buildConfiguration = "Release"

test/cpp/end2end/async_end2end_test.cc

@@ -484,6 +484,81 @@ TEST_P(AsyncEnd2endTest, SimpleClientStreaming) {
   EXPECT_TRUE(recv_status.ok());
 }
 
+// Two pings and a final pong.
+TEST_P(AsyncEnd2endTest, SimpleClientStreamingWithCoalescingApi) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncReader<EchoResponse, EchoRequest> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  cli_ctx.set_initial_metadata_corked(true);
+  // tag:1 never comes up since no op is performed
+  std::unique_ptr<ClientAsyncWriter<EchoRequest>> cli_stream(
+      stub_->AsyncRequestStream(&cli_ctx, &recv_response, cq_.get(), tag(1)));
+
+  service_.RequestRequestStream(&srv_ctx, &srv_stream, cq_.get(), cq_.get(),
+                                tag(2));
+
+  cli_stream->Write(send_request, tag(3));
+
+  // 65536(64KB) is the default flow control window size. Should change this
+  // number when default flow control window size changes. For the write of
+  // send_request larger than the flow control window size, tag:3 will not come
+  // up until server read is initiated. For write of send_request smaller than
+  // the flow control window size, the request can take the free ride with
+  // initial metadata due to coalescing, thus write tag:3 will come up here.
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking)
+        .Expect(2, true)
+        .Expect(3, true)
+        .Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking).Expect(2, true).Verify(cq_.get());
+  }
+
+  srv_stream.Read(&recv_request, tag(4));
+
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking).Expect(4, true).Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking)
+        .Expect(3, true)
+        .Expect(4, true)
+        .Verify(cq_.get());
+  }
+
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  cli_stream->WriteLast(send_request, WriteOptions(), tag(5));
+  srv_stream.Read(&recv_request, tag(6));
+  Verifier(GetParam().disable_blocking)
+      .Expect(5, true)
+      .Expect(6, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  srv_stream.Read(&recv_request, tag(7));
+  Verifier(GetParam().disable_blocking).Expect(7, false).Verify(cq_.get());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.Finish(send_response, Status::OK, tag(8));
+  cli_stream->Finish(&recv_status, tag(9));
+  Verifier(GetParam().disable_blocking)
+      .Expect(8, true)
+      .Expect(9, true)
+      .Verify(cq_.get());
+
+  EXPECT_EQ(send_response.message(), recv_response.message());
+  EXPECT_TRUE(recv_status.ok());
+}
+
 // One ping, two pongs.
 TEST_P(AsyncEnd2endTest, SimpleServerStreaming) {
   ResetStub();
@@ -540,6 +615,112 @@ TEST_P(AsyncEnd2endTest, SimpleServerStreaming) {
   EXPECT_TRUE(recv_status.ok());
 }
 
+// One ping, two pongs. Using WriteAndFinish API
+TEST_P(AsyncEnd2endTest, SimpleServerStreamingWithCoalescingApiWAF) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncWriter<EchoResponse> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  std::unique_ptr<ClientAsyncReader<EchoResponse>> cli_stream(
+      stub_->AsyncResponseStream(&cli_ctx, send_request, cq_.get(), tag(1)));
+
+  service_.RequestResponseStream(&srv_ctx, &recv_request, &srv_stream,
+                                 cq_.get(), cq_.get(), tag(2));
+
+  Verifier(GetParam().disable_blocking)
+      .Expect(1, true)
+      .Expect(2, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.Write(send_response, tag(3));
+  cli_stream->Read(&recv_response, tag(4));
+  Verifier(GetParam().disable_blocking)
+      .Expect(3, true)
+      .Expect(4, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  srv_stream.WriteAndFinish(send_response, WriteOptions(), Status::OK, tag(5));
+  cli_stream->Read(&recv_response, tag(6));
+  Verifier(GetParam().disable_blocking)
+      .Expect(5, true)
+      .Expect(6, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Read(&recv_response, tag(7));
+  Verifier(GetParam().disable_blocking).Expect(7, false).Verify(cq_.get());
+
+  cli_stream->Finish(&recv_status, tag(8));
+  Verifier(GetParam().disable_blocking).Expect(8, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
+// One ping, two pongs. Using WriteLast API
+TEST_P(AsyncEnd2endTest, SimpleServerStreamingWithCoalescingApiWL) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncWriter<EchoResponse> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  std::unique_ptr<ClientAsyncReader<EchoResponse>> cli_stream(
+      stub_->AsyncResponseStream(&cli_ctx, send_request, cq_.get(), tag(1)));
+
+  service_.RequestResponseStream(&srv_ctx, &recv_request, &srv_stream,
+                                 cq_.get(), cq_.get(), tag(2));
+
+  Verifier(GetParam().disable_blocking)
+      .Expect(1, true)
+      .Expect(2, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.Write(send_response, tag(3));
+  cli_stream->Read(&recv_response, tag(4));
+  Verifier(GetParam().disable_blocking)
+      .Expect(3, true)
+      .Expect(4, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  srv_stream.WriteLast(send_response, WriteOptions(), tag(5));
+  cli_stream->Read(&recv_response, tag(6));
+  srv_stream.Finish(Status::OK, tag(7));
+  Verifier(GetParam().disable_blocking)
+      .Expect(5, true)
+      .Expect(6, true)
+      .Expect(7, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Read(&recv_response, tag(8));
+  Verifier(GetParam().disable_blocking).Expect(8, false).Verify(cq_.get());
+
+  cli_stream->Finish(&recv_status, tag(9));
+  Verifier(GetParam().disable_blocking).Expect(9, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
 // One ping, one pong.
 TEST_P(AsyncEnd2endTest, SimpleBidiStreaming) {
   ResetStub();
@@ -599,6 +780,144 @@ TEST_P(AsyncEnd2endTest, SimpleBidiStreaming) {
   EXPECT_TRUE(recv_status.ok());
 }
 
+// One ping, one pong. Using server:WriteAndFinish api
+TEST_P(AsyncEnd2endTest, SimpleBidiStreamingWithCoalescingApiWAF) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncReaderWriter<EchoResponse, EchoRequest> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  cli_ctx.set_initial_metadata_corked(true);
+  std::unique_ptr<ClientAsyncReaderWriter<EchoRequest, EchoResponse>>
+      cli_stream(stub_->AsyncBidiStream(&cli_ctx, cq_.get(), tag(1)));
+
+  service_.RequestBidiStream(&srv_ctx, &srv_stream, cq_.get(), cq_.get(),
+                             tag(2));
+
+  cli_stream->WriteLast(send_request, WriteOptions(), tag(3));
+
+  // 65536(64KB) is the default flow control window size. Should change this
+  // number when default flow control window size changes. For the write of
+  // send_request larger than the flow control window size, tag:3 will not come
+  // up until server read is initiated. For write of send_request smaller than
+  // the flow control window size, the request can take the free ride with
+  // initial metadata due to coalescing, thus write tag:3 will come up here.
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking)
+        .Expect(2, true)
+        .Expect(3, true)
+        .Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking).Expect(2, true).Verify(cq_.get());
+  }
+
+  srv_stream.Read(&recv_request, tag(4));
+
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking).Expect(4, true).Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking)
+        .Expect(3, true)
+        .Expect(4, true)
+        .Verify(cq_.get());
+  }
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  srv_stream.Read(&recv_request, tag(5));
+  Verifier(GetParam().disable_blocking).Expect(5, false).Verify(cq_.get());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.WriteAndFinish(send_response, WriteOptions(), Status::OK, tag(6));
+  cli_stream->Read(&recv_response, tag(7));
+  Verifier(GetParam().disable_blocking)
+      .Expect(6, true)
+      .Expect(7, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Finish(&recv_status, tag(8));
+  Verifier(GetParam().disable_blocking).Expect(8, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
+// One ping, one pong. Using server:WriteLast api
+TEST_P(AsyncEnd2endTest, SimpleBidiStreamingWithCoalescingApiWL) {
+  ResetStub();
+
+  EchoRequest send_request;
+  EchoRequest recv_request;
+  EchoResponse send_response;
+  EchoResponse recv_response;
+  Status recv_status;
+  ClientContext cli_ctx;
+  ServerContext srv_ctx;
+  ServerAsyncReaderWriter<EchoResponse, EchoRequest> srv_stream(&srv_ctx);
+
+  send_request.set_message(GetParam().message_content);
+  cli_ctx.set_initial_metadata_corked(true);
+  std::unique_ptr<ClientAsyncReaderWriter<EchoRequest, EchoResponse>>
+      cli_stream(stub_->AsyncBidiStream(&cli_ctx, cq_.get(), tag(1)));
+
+  service_.RequestBidiStream(&srv_ctx, &srv_stream, cq_.get(), cq_.get(),
+                             tag(2));
+
+  cli_stream->WriteLast(send_request, WriteOptions(), tag(3));
+
+  // 65536(64KB) is the default flow control window size. Should change this
+  // number when default flow control window size changes. For the write of
+  // send_request larger than the flow control window size, tag:3 will not come
+  // up until server read is initiated. For write of send_request smaller than
+  // the flow control window size, the request can take the free ride with
+  // initial metadata due to coalescing, thus write tag:3 will come up here.
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking)
+        .Expect(2, true)
+        .Expect(3, true)
+        .Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking).Expect(2, true).Verify(cq_.get());
+  }
+
+  srv_stream.Read(&recv_request, tag(4));
+
+  if (GetParam().message_content.length() < 65536) {
+    Verifier(GetParam().disable_blocking).Expect(4, true).Verify(cq_.get());
+  } else {
+    Verifier(GetParam().disable_blocking)
+        .Expect(3, true)
+        .Expect(4, true)
+        .Verify(cq_.get());
+  }
+  EXPECT_EQ(send_request.message(), recv_request.message());
+
+  srv_stream.Read(&recv_request, tag(5));
+  Verifier(GetParam().disable_blocking).Expect(5, false).Verify(cq_.get());
+
+  send_response.set_message(recv_request.message());
+  srv_stream.WriteLast(send_response, WriteOptions(), tag(6));
+  srv_stream.Finish(Status::OK, tag(7));
+  cli_stream->Read(&recv_response, tag(8));
+  Verifier(GetParam().disable_blocking)
+      .Expect(6, true)
+      .Expect(7, true)
+      .Expect(8, true)
+      .Verify(cq_.get());
+  EXPECT_EQ(send_response.message(), recv_response.message());
+
+  cli_stream->Finish(&recv_status, tag(9));
+  Verifier(GetParam().disable_blocking).Expect(9, true).Verify(cq_.get());
+
+  EXPECT_TRUE(recv_status.ok());
+}
+
 // Metadata tests
 TEST_P(AsyncEnd2endTest, ClientInitialMetadataRpc) {
   ResetStub();

test/cpp/end2end/end2end_test.cc

@@ -702,6 +702,21 @@ TEST_P(End2endTest, RequestStreamOneRequest) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, RequestStreamOneRequestWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+
+  context.set_initial_metadata_corked(true);
+  auto stream = stub_->RequestStream(&context, &response);
+  request.set_message("hello");
+  stream->WriteLast(request, WriteOptions());
+  Status s = stream->Finish();
+  EXPECT_EQ(response.message(), request.message());
+  EXPECT_TRUE(s.ok());
+}
+
 TEST_P(End2endTest, RequestStreamTwoRequests) {
   ResetStub();
   EchoRequest request;
@@ -718,6 +733,22 @@ TEST_P(End2endTest, RequestStreamTwoRequests) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, RequestStreamTwoRequestsWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+
+  context.set_initial_metadata_corked(true);
+  auto stream = stub_->RequestStream(&context, &response);
+  request.set_message("hello");
+  EXPECT_TRUE(stream->Write(request));
+  stream->WriteLast(request, WriteOptions());
+  Status s = stream->Finish();
+  EXPECT_EQ(response.message(), "hellohello");
+  EXPECT_TRUE(s.ok());
+}
+
 TEST_P(End2endTest, ResponseStream) {
   ResetStub();
   EchoRequest request;
@@ -738,6 +769,27 @@ TEST_P(End2endTest, ResponseStream) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, ResponseStreamWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+  request.set_message("hello");
+  context.AddMetadata(kServerUseCoalescingApi, "1");
+
+  auto stream = stub_->ResponseStream(&context, request);
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message() + "0");
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message() + "1");
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message() + "2");
+  EXPECT_FALSE(stream->Read(&response));
+
+  Status s = stream->Finish();
+  EXPECT_TRUE(s.ok());
+}
+
 TEST_P(End2endTest, BidiStream) {
   ResetStub();
   EchoRequest request;
@@ -770,6 +822,39 @@ TEST_P(End2endTest, BidiStream) {
   EXPECT_TRUE(s.ok());
 }
 
+TEST_P(End2endTest, BidiStreamWithCoalescingApi) {
+  ResetStub();
+  EchoRequest request;
+  EchoResponse response;
+  ClientContext context;
+  context.AddMetadata(kServerFinishAfterNReads, "3");
+  context.set_initial_metadata_corked(true);
+  grpc::string msg("hello");
+
+  auto stream = stub_->BidiStream(&context);
+
+  request.set_message(msg + "0");
+  EXPECT_TRUE(stream->Write(request));
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message());
+
+  request.set_message(msg + "1");
+  EXPECT_TRUE(stream->Write(request));
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message());
+
+  request.set_message(msg + "2");
+  stream->WriteLast(request, WriteOptions());
+  EXPECT_TRUE(stream->Read(&response));
+  EXPECT_EQ(response.message(), request.message());
+
+  EXPECT_FALSE(stream->Read(&response));
+  EXPECT_FALSE(stream->Read(&response));
+
+  Status s = stream->Finish();
+  EXPECT_TRUE(s.ok());
+}
+
 // Talk to the two services with the same name but different package names.
 // The two stubs are created on the same channel.
 TEST_P(End2endTest, DiffPackageServices) {

test/cpp/end2end/mock_test.cc

@@ -89,7 +89,7 @@ class MockClientReaderWriter<EchoRequest, EchoResponse> final
     return true;
   }
 
-  bool Write(const EchoRequest& msg, const WriteOptions& options) override {
+  bool Write(const EchoRequest& msg, WriteOptions options) override {
     gpr_log(GPR_INFO, "mock recv msg %s", msg.message().c_str());
     last_message_ = msg.message();
     return true;

test/cpp/end2end/test_service_impl.cc

@@ -246,6 +246,9 @@ Status TestServiceImpl::ResponseStream(ServerContext* context,
   int server_try_cancel = GetIntValueFromMetadata(
       kServerTryCancelRequest, context->client_metadata(), DO_NOT_CANCEL);
 
+  int server_coalescing_api = GetIntValueFromMetadata(
+      kServerUseCoalescingApi, context->client_metadata(), 0);
+
   if (server_try_cancel == CANCEL_BEFORE_PROCESSING) {
     ServerTryCancel(context);
     return Status::CANCELLED;
@@ -260,7 +263,11 @@ Status TestServiceImpl::ResponseStream(ServerContext* context,
 
   for (int i = 0; i < kNumResponseStreamsMsgs; i++) {
     response.set_message(request->message() + grpc::to_string(i));
-    writer->Write(response);
+    if (i == kNumResponseStreamsMsgs - 1 && server_coalescing_api != 0) {
+      writer->WriteLast(response, WriteOptions());
+    } else {
+      writer->Write(response);
+    }
   }
 
   if (server_try_cancel_thd != nullptr) {
@@ -305,10 +312,21 @@ Status TestServiceImpl::BidiStream(
         new std::thread(&TestServiceImpl::ServerTryCancel, this, context);
   }
 
+  // kServerFinishAfterNReads suggests after how many reads, the server should
+  // write the last message and send status (coalesced using WriteLast)
+  int server_write_last = GetIntValueFromMetadata(
+      kServerFinishAfterNReads, context->client_metadata(), 0);
+
+  int read_counts = 0;
   while (stream->Read(&request)) {
+    read_counts++;
     gpr_log(GPR_INFO, "recv msg %s", request.message().c_str());
     response.set_message(request.message());
-    stream->Write(response);
+    if (read_counts == server_write_last) {
+      stream->WriteLast(response, WriteOptions());
+    } else {
+      stream->Write(response);
+    }
   }
 
   if (server_try_cancel_thd != nullptr) {

test/cpp/end2end/test_service_impl.h

@@ -48,6 +48,8 @@ const int kNumResponseStreamsMsgs = 3;
 const char* const kServerCancelAfterReads = "cancel_after_reads";
 const char* const kServerTryCancelRequest = "server_try_cancel";
 const char* const kDebugInfoTrailerKey = "debug-info-bin";
+const char* const kServerFinishAfterNReads = "server_finish_after_n_reads";
+const char* const kServerUseCoalescingApi = "server_use_coalescing_api";
 
 typedef enum {
   DO_NOT_CANCEL = 0,

test/cpp/microbenchmarks/bm_fullstack_streaming_ping_pong.cc

@@ -240,6 +240,173 @@ static void BM_StreamingPingPongMsgs(benchmark::State& state) {
   state.SetBytesProcessed(msg_size * state.iterations() * 2);
 }
 
+// Repeatedly makes Streaming Bidi calls (exchanging a configurable number of
+// messages in each call) in a loop on a single channel. Different from
+// BM_StreamingPingPong we are using stream coalescing api, e.g. WriteLast,
+// WriteAndFinish, set_initial_metadata_corked. These apis aim at saving
+// sendmsg syscalls for streaming by coalescing 1. initial metadata with first
+// message; 2. final streaming message with trailing metadata.
+//
+//  First parmeter (i.e state.range(0)):  Message size (in bytes) to use
+//  Second parameter (i.e state.range(1)): Number of ping pong messages.
+//      Note: One ping-pong means two messages (one from client to server and
+//      the other from server to client):
+//  Third parameter (i.e state.range(2)): Switch between using WriteAndFinish
+//  API and WriteLast API for server.
+template <class Fixture, class ClientContextMutator, class ServerContextMutator>
+static void BM_StreamingPingPongWithCoalescingApi(benchmark::State& state) {
+  const int msg_size = state.range(0);
+  const int max_ping_pongs = state.range(1);
+  // This options is used to test out server API: WriteLast and WriteAndFinish
+  // respectively, since we can not use both of them on server side at the same
+  // time. Value 1 means we are testing out the WriteAndFinish API, and
+  // otherwise we are testing out the WriteLast API.
+  const int write_and_finish = state.range(2);
+
+  EchoTestService::AsyncService service;
+  std::unique_ptr<Fixture> fixture(new Fixture(&service));
+  {
+    EchoResponse send_response;
+    EchoResponse recv_response;
+    EchoRequest send_request;
+    EchoRequest recv_request;
+
+    if (msg_size > 0) {
+      send_request.set_message(std::string(msg_size, 'a'));
+      send_response.set_message(std::string(msg_size, 'b'));
+    }
+
+    std::unique_ptr<EchoTestService::Stub> stub(
+        EchoTestService::NewStub(fixture->channel()));
+
+    while (state.KeepRunning()) {
+      ServerContext svr_ctx;
+      ServerContextMutator svr_ctx_mut(&svr_ctx);
+      ServerAsyncReaderWriter<EchoResponse, EchoRequest> response_rw(&svr_ctx);
+      service.RequestBidiStream(&svr_ctx, &response_rw, fixture->cq(),
+                                fixture->cq(), tag(0));
+
+      ClientContext cli_ctx;
+      ClientContextMutator cli_ctx_mut(&cli_ctx);
+      cli_ctx.set_initial_metadata_corked(true);
+      // tag:1 here will never comes up, since we are not performing any op due
+      // to initial metadata coalescing.
+      auto request_rw = stub->AsyncBidiStream(&cli_ctx, fixture->cq(), tag(1));
+
+      void* t;
+      bool ok;
+      int need_tags;
+
+      // Send 'max_ping_pongs' number of ping pong messages
+      int ping_pong_cnt = 0;
+      while (ping_pong_cnt < max_ping_pongs) {
+        if (ping_pong_cnt == max_ping_pongs - 1) {
+          request_rw->WriteLast(send_request, WriteOptions(), tag(2));
+        } else {
+          request_rw->Write(send_request, tag(2));  // Start client send
+        }
+
+        need_tags = (1 << 2) | (1 << 3) | (1 << 4) | (1 << 5);
+
+        if (ping_pong_cnt == 0) {
+          // wait for the server call structure (call_hook, etc.) to be
+          // initialized (async stream between client side and server side
+          // established). It is necessary when client init metadata is
+          // coalesced
+          GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+          while ((int)(intptr_t)t != 0) {
+            // In some cases tag:2 comes before tag:0 (write tag comes out
+            // first), this while loop is to make sure get tag:0.
+            int i = (int)(intptr_t)t;
+            GPR_ASSERT(need_tags & (1 << i));
+            need_tags &= ~(1 << i);
+            GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+          }
+        }
+
+        response_rw.Read(&recv_request, tag(3));   // Start server recv
+        request_rw->Read(&recv_response, tag(4));  // Start client recv
+
+        while (need_tags) {
+          GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+          GPR_ASSERT(ok);
+          int i = (int)(intptr_t)t;
+
+          // If server recv is complete, start the server send operation
+          if (i == 3) {
+            if (ping_pong_cnt == max_ping_pongs - 1) {
+              if (write_and_finish == 1) {
+                response_rw.WriteAndFinish(send_response, WriteOptions(),
+                                           Status::OK, tag(5));
+              } else {
+                response_rw.WriteLast(send_response, WriteOptions(), tag(5));
+                // WriteLast buffers the write, so neither server write op nor
+                // client read op will finish inside the while loop.
+                need_tags &= ~(1 << 4);
+                need_tags &= ~(1 << 5);
+              }
+            } else {
+              response_rw.Write(send_response, tag(5));
+            }
+          }
+
+          GPR_ASSERT(need_tags & (1 << i));
+          need_tags &= ~(1 << i);
+        }
+
+        ping_pong_cnt++;
+      }
+
+      if (max_ping_pongs == 0) {
+        need_tags = (1 << 6) | (1 << 7) | (1 << 8);
+      } else {
+        if (write_and_finish == 1) {
+          need_tags = (1 << 8);
+        } else {
+          // server's buffered write and the client's read of the buffered write
+          // tags should come up.
+          need_tags = (1 << 4) | (1 << 5) | (1 << 7) | (1 << 8);
+        }
+      }
+
+      // No message write or initial metadata write happened yet.
+      if (max_ping_pongs == 0) {
+        request_rw->WritesDone(tag(6));
+        // wait for server call data structure(call_hook, etc.) to be
+        // initialized, since initial metadata is corked.
+        GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+        while ((int)(intptr_t)t != 0) {
+          int i = (int)(intptr_t)t;
+          GPR_ASSERT(need_tags & (1 << i));
+          need_tags &= ~(1 << i);
+          GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+        }
+        response_rw.Finish(Status::OK, tag(7));
+      } else {
+        if (write_and_finish != 1) {
+          response_rw.Finish(Status::OK, tag(7));
+        }
+      }
+
+      Status recv_status;
+      request_rw->Finish(&recv_status, tag(8));
+
+      while (need_tags) {
+        GPR_ASSERT(fixture->cq()->Next(&t, &ok));
+        int i = (int)(intptr_t)t;
+        GPR_ASSERT(need_tags & (1 << i));
+        need_tags &= ~(1 << i);
+      }
+
+      GPR_ASSERT(recv_status.ok());
+    }
+  }
+
+  fixture->Finish(state);
+  fixture.reset();
+  state.SetBytesProcessed(msg_size * state.iterations() * max_ping_pongs * 2);
+}
+
 /*******************************************************************************
  * CONFIGURATIONS
  */
@@ -270,6 +437,30 @@ BENCHMARK_TEMPLATE(BM_StreamingPingPongMsgs, InProcessCHTTP2, NoOpMutator,
 BENCHMARK_TEMPLATE(BM_StreamingPingPongMsgs, TCP, NoOpMutator, NoOpMutator)
     ->Range(0, 128 * 1024 * 1024);
 
+// Generate Args for StreamingPingPongWithCoalescingApi benchmarks. Currently
+// generates args for only "small streams" (i.e streams with 0, 1 or 2 messages)
+static void StreamingPingPongWithCoalescingApiArgs(
+    benchmark::internal::Benchmark* b) {
+  int msg_size = 0;
+
+  b->Args(
+      {0, 0, 0});  // spl case: 0 ping-pong msgs (msg_size doesn't matter here)
+  b->Args(
+      {0, 0, 1});  // spl case: 0 ping-pong msgs (msg_size doesn't matter here)
+
+  for (msg_size = 0; msg_size <= 128 * 1024 * 1024;
+       msg_size == 0 ? msg_size++ : msg_size *= 8) {
+    b->Args({msg_size, 1, 0});
+    b->Args({msg_size, 2, 0});
+    b->Args({msg_size, 1, 1});
+    b->Args({msg_size, 2, 1});
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_StreamingPingPongWithCoalescingApi, InProcessCHTTP2,
+                   NoOpMutator, NoOpMutator)
+    ->Apply(StreamingPingPongWithCoalescingApiArgs);
+
 }  // namespace testing
 }  // namespace grpc